The engineer and I had just spent several hours balancing rhythm tracks but the bass guitar was still not out front enough. I asked for more bass, but he turned to me and said, "That's as loud as we can get it." He reached up and hit the solo button on the mixer for the bass channel and pointed to the meters. Sure enough, all on its own the bass guitar was right on the verge of overdriving the board. But when those other instruments were turned back on you couldn't hear it. It was the first time I'd ever seen a visual demonstration of the limits of ever-increasing volume in the mix. The bass was as loud as we could get it without distortion, but the other instruments were masking the sound. And I had just learned a lesson that was useful far beyond the recording studio.
Subtractive Mixing - The Basics
Start with the understanding that there is only a limited amount of available space in the mix. As you add instruments or increase their volume you are using up that space and it won't be available for the rest of the mix. Once two or more instruments are competing for the same space you need to prioritize one over the other, or try to move them out of one another's way. The basic concept of Subtractive Mixing is to identify the frequency ranges each of the tracks "lives in" and then group the tracks into frequency "families" which must live well together, then carefully balance all the tracks in each range to achieve harmony between them.
Creating a Nominal Reference Point
Set your primary rhythm tracks at nominal to begin the process. These will usually be kick and snare in most pop music. You'll need to make an educated guess as to the relative volume balance and EQ of each primary rhythm track. Because these tracks are likely to be ones you'll want to be prominent in the final mix, they make a good gauge of how close you are to running out of space. If the kick goes away or the snare looses authority you've reached the limit. Begin adding your rhythm section one instrument at a time with the objective of achieving a mix where you can hear everything, and be stingy with volume. As soon as the track sits in the mix, stop and leave the level there. While adding instruments, notice which family of instruments have the same frequency range. These are the instruments we will be balancing later to get them to behave well together. Pay special attention to the way that the other instruments in the same family can affect each other's tone as well. For example, too much bass can bury your kick and take the crunch away from your guitars. The reason this happens is because those instruments are sharing some of the exact same frequencies and your ear naturally picks out the loudest instrument at each frequency. Try experimenting by raising and lowering the levels while noticing how it affects the sound of the tracks, and taking note of which parts you want to make a priority and which conflicts you need to resolve.
Use Subtractive Mixing to Unmask the Hidden Part
When you notice a track is getting buried in the mix, avoid simply turning it up because this disrupts the balance you've worked so hard to achieve. Instead start by lowering (or subtracting) the level from one or more of the other tracks in that family. Sometimes all you need to do is lower one instrument to make several others sound much better. But there are limits so you must keep your expectations reasonable. Keep track of your original starting point and remember to add back anything that didn't make space for the part you want to highlight. If the adjustment you made didn't help, put it back the way it was. Once you have got the families of tracks working well together, you can start the same process mixing them into a final mix.
Taking it the Rest of the Way
But what if the tracks won't work together no matter what I do? Can I move them to a different range? Absolutely! In Part 2 of this series where we will talk about applying the same principle to EQ adjustments in order to move tracks laterally out of each other's way without lowering the level. We'll also talk about how to use these concepts to master mixing from the backline without instruments in the PA system. Try experimenting with different levels in each group and listening for the ways those changes also affect the tone of your instruments. Listening as you balance the tracks will help you notice the crucial aspects of each track, and you will be better equipped to make adjustments without losing them.
Have you ever tried Subtractive Mixing? What benefits did you notice? Let us know in the comments below.
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